Furnace



May 3, 1938. A; c. MUiR ET AL .2,116,322

FURNACE Filed Aug. 29, 193e,

4 Sheets-Sheet 1 Patented May 3, 1938 FURNACE Andrew C. Muir, Lansdowne,and William C.

Griffiths, Narberth, Pa.

Application August Z9, 1936, Serial No. 98,570

Claims.

which is at once easy and inexpensive to manufacture and well suited tothe needs of service.

A further purpose is to provide a reciprocating grate with major andminor air passages, to by pass the grate and to close the major airpassages when the grate is bypassed.

A further purpose is to control the pressure drop through a fuel bed,and thereby the rate of fuel combustion, by suitable back and forthshiftings of a grate supporting the fuel.

-A further purpose is to determine the high and low combustion rates ofa thermostatically controlled furnace by thermostatically shifting thevfuel bed, to close and open respectively a space beyond the grate whichconnects the fire chamber to the ash chamber.

A further purpose is to aid the delivery of ashes out of a' fuel bedinto an. ash compartment by back and forth shiftings of a gratesupporting the fuel bed to positions that respectively determine highand low rates of combustion.

A further purpose is to operate a stoker and the back and forth shiftingof a grate by thermostatically controlled common mechanism usingsuccessive shiftings of the grate to successively increase and check therate of heat development and the corresponding retracting and feedingstrokes of the Stoker to 'add fuel to the furnace` with each checking ofthe furnace.

A further purpose is to operate the stoker at time intervals while thethermostat is in the more heat position. i

A further purpose is to provide novel, effective and inexpensivemechanism respectively for supporting a bed of burning fuel and foradding fresh' fuel, preferably each timethe furnace is put on highheating, and during high heating.

Further purposes will appear in the specification and in the claims. ,yWe have elected to show one only of the differ- V ent forms of ourinvention, selecting a form however that is practical and eicent inoperation and which well illustrates the principles involved.

Figure 1 is a vertical section to illustrate a desirable embodiment ofthe invention as applied to a domestic heater. In its more broadfeatures the heater illustrationis'intended for a conventionalillustration of any heater `to which the invention may be applied. Thegrate is in the 5 draft bypass position in Figure 1. i

Figure 1a. is Va diagrammatic view of the electric circuit. I

Figure 2 is a horizontal section of Figure 1, taken upon the line 2-2thereof and to enlarged 10 scale. Y

Figures 3 and 4 are Ydetail sections of Figure 2, upon the lines 3--3and 4--4 thereof respectively, to show supporting mechanismof thefurnace floor, as well as draft bypass.

Figure 5 is a left side el 4vation of Figure 1. omitting motor andthermostatic control equipment shown in Figure 1.

Figure 6 is a broken vertical sectioncorresponding to a portionof Figure1 but with the 20 hopper structureof Figure 1 not shown in Figure 6, thehopper having been wheeled aside for hand firing. The grate is in thehigh combustion position in Figure 6.

Figure 7 is a left side elevation of Figure 6.

Like numerals refer to like parts in all figures.

Describing in illustration and not in limita.- ton and referring to thedrawings:-

Our invention relates toheaters of the type used for domestic heatingand for industrial installations, burning solid fuel such as anthracitecoal, bituminous coal; coke, petroleum coke, etc; The problem of'controlling the combustion in such heaters has received extensiveattention and has been solved in the main by the use of various doors,dampers,'etc., the correct use of which is an art only imperfectlyunderstood by the ordinary householder.

By our invention it is possible to greatly simplify the control ofdomestic heaters operating 40 on natural draft or on mechanical draft.The entire control of the heater is accomplished by changing theposition of the grate, and only grate positions corresponding with highheating or checking of the re aie necessary. 'The di- 45 culty of priorart shiftable grate constructions, that the grate air passages necessarywhen the fire is on high heating proves to be excessive when the fire ischecked, has been corrected by employing major and minor grate airpassages, bypassing the grate air passages by a passage of relativelyzero air friction compared to the' grate air passages when the fire'ischecked, and concurrently closing the major but not the minor grate' airpassages, and leaving the major and preferably some of the minor grateair passages open when the re is on high heating.

A furnace IIJ is shown as a water heater type, with ash and recompartments I I and I2 and the hot gases escaping to a chimney I3 byflue passages I4 to 20. 3The butterfly damper 2| is indi,- cated asbeing open, and the damper door 22 as being closed, since neither thebutterfly damper nor the damper door is used in control of the furnacein accord nce with our invention and they are illustrate; merely forcompleteness. A water space 23 surrounds the ue passages except atdoorways 25, 26 and 21 for poking, charging and clean out, respectively.Doorway 24 in the base is provided for ash removal.

A composite floor 28, separating the ash and re compartments, andreplacing any hitherto usual grate mechanism, is supported preferably onseveral posts 29 and 30 in the, ash pit, near opposite sides of thefront and rear thereof, respectively.v 'I'he posts 23 and 38 arepreferably flanged at 28' and 30. The composite floor, usuallypreferably horizontal, comprises a movable grate 3| and a stationarycentrally open framelike member 32 which peripherally fits the interiorof the 'furnace and at the front 33 and opposite sides 34 of its centralopening overlaps the front and sides-respectively of the grate 3|.

In its rearward position the gra-te, except for its own ai'r passages,closes the entire opening of the stationary member 33, the rearward edge35 of the grate then registering against the forwardly presented rearwall 33 of the opening as shown in-Figure 6.

In its forward position, as in Figure 1, the grate leaves an opening 31back of the grate and in front of the wall 33, which opening 31 willthen effectively check' the lire, since it reduces substantially to zerothe difference in pressure between the ash and fire compartments andtherefore the fall in pressure through the fuel bed.

We provide the grate with major and minor air' passages 38 and 33,lrespectively, in alternate laterally spaced transverse rows, with themaior passages 38 for use when the grate is rearward and therefore inits high heating position.. with the opening 31 closed, and the minor es33 for use when the grate is forward and therefore in its low heating ornre checking position. 'Ihis is accomplished by means of stationaryclosure strips 40 under and transversely across the grate and fasteningat their ends to grate-side-sulde portions 4I of the stationary member32. The

minor air passages are preferably tapered with variant with quite widelythe smaller opening at the top as shown so that ash entering them willreadily drop through.

The strips 48 are located to close the'rows of maior air passages 38when the. grate is in its forward position as shown in Figure 1. The airpassages are uncovered when the grate is moved back to its rearwardposition. Obviously the bm form and spacing and number for the airpassages 33 will be quite widely different fuels and free-burning willrequire than will be furnaces so that smaller sizes of or non-coking.coals, for example,

most suitable for larger fuel. y

We prefer to provide the movable grate with roller support. suitably oncasters supported in bearings 42 secured to the under-structure by bolts43 carrying spacing washers 44. l

Rear side rollers 45 are supported upon a `cross connection. suitably apipe 43 between the posts 33; forward side rollers 41 are supported upona cross connection 48 between the posts 29; and front rollers 48 aresupported upon branch members 58 from the cross members 48. The crossconnections 48 and 48, and side connections 5I, are integrated into astrong structure by ttings 52 which form parts of the posts 29 and 30.

'Ihe grate is shiftable back and forth, respectively, back into its highheating position and forward into its low heating or checking position,by any suitable means, such as hand manipulation or back and forthmovements of a rocker shaft 53, crank 54 thereon and link 55 connectingthe crank to a and rigidly fastened to the grate 3l. The rocker shaft 53is pivotally supported on posts 51.

The operation oi the grate may be purely manual and non-automatic. Forautomatic operation, if such be desired, we provide thermostaticallycontrolled means for operating the rocker shaft 53 and therefore forpositioning the grate for high or low heating according to the need orlack of need for high heating.

As illustrated in Figures 1a and l, a thermostat 58 controls theoperation of a reduction gear motor unit 53, connecting rod GI, has at62 a lost motion operative connection with an arm 63 fastened to therocker shaft 53. A stop switch 64, suitably operatively connectd to theshaft 53, as by a spring full-stroke connection 53', stops the motor atthe completion of each shift movement.

In the diagrammaticl electric connections of Figure 1a, the thermostat58 and the stop switch arm 84', pivoted at 842. connect to the motorterminals by conductors I5 and B6, suitably in series with a currentsource 81. A thermostat contact 63, with which connection is made whenmore heat is demanded, is connected by leads 68 and 63 with the contact883 of switch 64, and a thermostat contact 69 with which connection ismade when less heat is demanded, is connected by lead 83 with contact382 of switch 64. An aquastat switch 10 operatively connected to thewater temperature of the heater breaks connection between the more heat"wires 88', Gliz if or when the water temperature of the heater reachesany selected high linut, at the same time connecting the conductors 35and 63 to effect a "less heat shift of the grate if ever or whenever thewater temperature reaches this selected high limit.

We add fuel to the furnace at least once for each back and forthshifting cycle of the grate, preferably adding this charge of fresh fueleach time the grate moves rearward into its position for highcombustion, since in this position the grate has 'progressed the fuelbed toward the rearward end of the grate, leaving space at theV"forward'end for fresh fuel.

In order to provide for the supply of successive increments of fuel incase the thermostat remains in the more heat position for a substantialperiod of time, it has been found desirable to operate the stoker atpredetermined time intervals while the thermostat continues to demandmore heat. In Figure la. a time switch 1I is shown having a rotatableswitch arm 1I' driven in one direction by a time clock 12. The switcharm 'Il' passes over any suitable number of contacts 1I?, 1I. '|I4, 1I.1I, 'II'l which are suitably connected through switches 13', 132, 133,134, 13', 13 to a lead 14 extending to the lead 65. A lead 15 likewiseextends from the switch arm 1 I to the lead 33'. Any of the contacts 1|2to 1V' may be rendered ineffective by opening the corresponding switch13' to 13.

yoke 56 extending downward fromwhich, through a crank 60 and Asillustrated Va hopper `16 is removably mounted to present the open end11 of its delivery `livery mechanism per at the sides spout 18 into anopening 19 cut in the furnace charging door 80, an auxiliary door 8|normally closing the opening 19 when the hopper is out of its operatingposition in front of the furnace. As illustrated, the auxiliary door 8|has alternative lug supports at 82 and 83, respectively, on the chargingdoor and on the furnace wall above the charging door.

vThe hopper 16 is mounted on means of suitable frame structure 85. Thedeincludes a' movable stoking plate. 86 that in effect forms a bottom ofthe hopper shaping toward the furnace. The stoking plate is preferablyroller supported, as at 81, and is shifted from the rocker shaft 53 thatshifts the grate, preferably toward the furnace each time the grate isshifted rearward into its more heat position and away from the furnaceeach time the grate is shifted to its less heat position.

A vertically adjustable gate 88 in the delivery spout extendingdownwardly fromithe roof thereof enables the operator to properly relatethe fuel feed to the rate of combustion within the furnace. i

The operating mechanism between the rocker shaft 53 and the stokingplate 86, as shown, includes a rocker shaft 89 plvotally supported at 90on the frame structure 85, having crank and link connection at 9| and 92with a downward lug 93 from Ithe stoking plate 86, and having crank andlink connection at 94 and 95v with a crank 96 upon the rocker shaft 53.'I'he rocker shaft 53 is thus a common shifter for the grate 3| and forthe stoking plate 86.

We preferably provide a catch compartment 91 below the stoking plate, tocatch fuel dust and fuel particles that may escape from the hopandforward end of the shifting stoking plate. ment 91 far enough at 98 toinclose the end 99 of the stoking plate when the plate is retracted toits furthermost position.

A bottom slide |00 of the catch compartment permits an easy periodiccleaning out of the compartment. For -easy assembly and disassembly,each of the links 55, and 92 mayhave hook connection with eitheror bothof the cranks driving it and the member that it in turn drives.

The distance of the shifting movements of the grate 3| and of thestoking plate 86 may be adjusted together by adjusting the lost motionlat one or both of the stops 62, to adjust the reciprocating action Vofthe rocker shaft 53, and, if desired, either the grate or the stokingplate may be adjusted separately by an adjustment of the effectivelength of one or more of the appropriate cranks 54, 9|,'94 or 96, asindicated at |0| for the crank 94. The effective length of the link 95may be adjusted at |0| for any effective length of the crank 94.

' hand firing or When it is desired to move the hopper assembly awayfrom before the furnace, as for continuous for an initial building of afire, Aor to fill the' hopper at the coal bin, the link 95 isdisconnected from the crank 94, as by unhooking, and any blocking of thewheels 84 is removed,

after which the hopper assembly will readily wheel away. If desired thehopper may be entirely omitted.

It will be seen that when the hopper assembly -is in place before thefurnace, it seals therewith at a gasket |02. suitably of asbestos,compressed wheels s4 bv' We extend the catch compartair around the fuelbedis now closed.

v 3 between the furnace `door and a peripheral shoulder |03 of thehopper spout 18.

While the contour of the burning fuel bed will vary quite widely withdifferent fuel characteristics as well as with different operatinglconditions that will make essential different adjustments at the gate88, a typical contour may be about as indicated by the line |04, Figure1;

The manual operation of the device is vvery simple when the hopper 16 isnot used. Any suitable solid fuel such as hard or soft coal, coke orpetroleum coke of any one of the commercial sizes burned in domesticheaters is chargedfrom time to time at the upper end of the fuel bed|04. As long as it is desired to check the fire, the grate 3| remains inits forward position as shown in Figure I. The air then passes almostentirely through the bypass opening 31 between the end of the grate andthe edge 36 of the rear plate. 'I'he closure strips 40 preventsubstantial flow of air through the major grate air passages 39, thusavoiding the diliicultyl that substantial flow of air will take placethrough the grate and cause burning up of the relatively thin end |04 ofthe fuel bed when the fire is intended to be checked. Substantially theonly air passing through thefuel bed when the lre is checked is thatpassing through the minor ,grate air passages 39 and causing verygradual combustion at the relatively thin end |04' of the fuel bed.

If now' it be desired to obtain high heating from the fire, grate 3| maybe slid manually to its rearward position as shown in Figure 6, therebyuncovering the major grate air passages 38 (and incidentally obstructingsome of the minor grate air'passages 39 which are relatively unimportantat this time). Air passing from the ash chamber to the )combustionchamber must now pass through the major grate air passages 38 and suchof the minor grate air passages 39 as remain open, thus causing vigorouscombustion, as the opening 31 which formerly bypassed the 'tity of ashat the rearmost end of the grate drops into the ash pit, where it 'canbe removed manually or mechanically asdesired, in any well known manner.

'It will be noted that the buttery damper 2|, damper door 22 and thevarious -furnace doors have no function whatever in the control of thefire, which is controlled wholly by movement of the grate to one or theother of its limiting positions. The doorway 24 is continuously open,and the doorways 25 and 26 are continuously closed except for thecharging opening in the doorway 26 which will normally be connected withthe hopper. It is intended to maintain the hopper sufficiently full offuel so that air will not enter shifted the grate to its forwardposition as seen in Figure 1, let' us assume that the thermostat 58demands more heat, thus moving to a position touching contact 68. Thiscompletes a circuit from the source 61 through the lead 66, the motor,the lead 65, the thermostat 58, the lead 68', the aquastat contacts, thelead 68, the switch contact 683, the switch arm 64' in the positionshown in Figure 1, and the lead 66.

'I'he motor starts up, moving the crank 60 clockwise for example for ahalf revolution, and thus carrying the connecting rod 6|, the crank 63,the rocker 53, the crank 54, the link 55, the lug 56 and the grate 3| tothe position of Figure 6. Actually the connecting rod 6| moves muchfarther than the link 55, but the overtravel is taken care of by thelost motion connection 62 which is adjusted so that the latter part ofthe stroke of the connecting rod 6| will be operative to move the grate.

'I'he motion of rocker shaft 53 as it travels beyond its intermediateposition will move full stroke device 53' and throw switch arm 64' to aposition against switch contact 692, thus breaking the motor circuit andcausing the motor to stop. By selection of a motor and gear reductionhaving sufcient friction, it is possible tomake the motor stop reliablyat the half circumference, although if desired a spring detent |05 maybe made to engage in one of the slots |86 of the crank disc to limit thestroke to a half revolution. The contact between the switch arm 64' andthe contact 692 is at thispoint ineiective to re-start the motor becausethe thermostat is presumably still demanding more heat.

At the same time that the rocker shaft 53 turns to shift the grate 3| toits rearward position, it likewise moves the stoker plate 86 to itsfeeding position by imparting motion to the crank 96, link 95, crank 94,rocker shaft 89, crank 9|, link 92 and lug 93.

Unless the time switch 1| closes the circuit between the leads 65 and69', the stoker plate and grate remain in the position indicated untilthe ythermostat 58 demands less heat and thus completes the motorcircuit from the source 61 through lead 66, the motor, lead'65, contact69, lead 69', contact 692, switch arm 64 and lead 66, thus causing themotor to travel another half revolution in the same direction and movethe grate and stoker plate from the position of Figure 6 back to theposition of Figure 1, concurrently dropping oil ash from the end oi' thegrate and retracting the stoker plate.

Assuming that the thermostat is in the "more heat position and hasshifted the grate to the corresponding position as shown in Figure 6,and assuming that the climatic condition is such that more heat" isdemanded for a substantial period of time,.the time switch arm 1|' willafter a predetermined time interval touch one of the contacts 1|2 to 1|?whose corresponding switch 13 to. 13 is closed, thus completing thecircuit between the leads 65 and 69', and operating the motor to movethe grate into the less heat position as shown in Figure 1, to chargethe stoker plate and to move the switch arm 64' Figure 1a.

If during the interval of shifting of the gate Y to the position of lcurrrently operate the Stoker plate to feed a charge of fuel to thefire. This series of operations will be repeated while the thermostatdemands more heat, as long and as often as the time switch arm 1|'touches a contact 1|2 to 1| 7 whose corresponding switch 13 to 136 isclosed.

In this way it is possible to provide repeated charges of fuel duringthe period that the thermostat is demanding more heat Without any shiftin the thermostat position. The number of charges of fuel supplied in agiven time may be varied by changing the size of the contacts 1|z to1|'I and by opening and closing the switches 13' to 13.

The fresh charges of fuel are successively carried rearward along thegrate by the successive rearward movements of heating position. l

An important feature of the invention is the use of major grate airpassages when the fire is on high heating and the closure of the majorgrate air passages when the grate air passages are bypassed and the reis checked.

Since the invention is intended particularly to apply to domesticheaters, it will be evident that it affords a very convenient means ofcontrolling such heaters, dispensing with the numerous dampers andchecks which have previously been used.

In view of our invention and disclosure, variations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled inthe art to obtain part or all of the benefits of ourinvention without copying the structure shown, and we, therefore, claimall such in so far as they fall within the reasonable spirit and scopeof our invention.

Having thus described our invention, what we claim as new and desire tosecure by Letters Patent is:

1. A furnace having fire and ash compartments and a composite gratebetween the compartments comprising relatively movable members, saidgrate having openings at intervals which are open in one position of themembers for passing air through the fuel bed and having a by-passopening which is open in another position of the members for by-passingair around the fuel bed,-

normally supporting the main body of the fuel,.

and structure sealing 4against the back edge of the grate in the backposition thereof and leaving a byrpass opening between lthe' structureand the grate in the forward position thereof and sealing the side andforward portions of the grate in both positions thereof andthermostatically controlled means for shifting the grate back and forthto determine respectively high and low rates of combustion, saidthermostatic means holding the grate in its', forward position as longas combustion is to' proceed at a low rate, and holding the grate in itsback position as long as combustion is to proceed at a high rate. .Y

- 3 A heater burning solid fuel including a grate the grate to its high.

having major and minor air passages, the grate being supported toreciprocate between limiting positions, there being a. bypass airopening around an edge of the grate when the grate is in a limitingposition corresponding with checking of the re and closure stripscooperating with the major air passages to restrict them when the graeis in the checking position, the -minor air openings being open when thegrate is in the checking position and the closure strips permitting themajor grate openings to open when the grate is in the position for highheating and the bypass opening is closed.

4. Afurnace burning solid fuel including agrate having sets of major andminor air passages,`

rollers beneath and supporting the grate, walls ylimiting the movementof the grate between a high heating and a checking position, closurestrips cooperating with the major air passages in the checking positionand uncovering the minor air openings in this position, there being abypass air opening behind the grate in the checking position, and theclosure strips uncovering the major air openings in the high heatingposition.

5. A furnace having fire and ash compartments and a composite floorbetween the compartments comprising a grate shiftable back 'and forthand for normally supporting the main body of the fuel, and structuresealing against the back edge of the grate in the back position thereofand sealing the side and forward; portions of the grate'in bothpositions thereof., the grate having major air passages and minor airpassages, closures under the grate registering with the major airpassages in one limiting position of the grate and uncoveringthe saidmajorair passages in another limiting position and thermostatically'controlled I means for shifting the grate back and forth between itslimiting positions which correspond with high and low rates ofcombustion.`

6. A heater burning solid fuel, including combustion and ash chambers,and including a grate having air passages and supported for movementbetween two limiting positions, provided at its rearward end with aby-pass opening between the combustion and the ash chamber to dischargeash and by-pass air when the grate is in its forward position, therebeing an opening for introduction of fuel at a substantial height abovethe grate at the forward end, thereby producing ari inclined fuel bedfrom the opening to the rear end of. the grate, a thermostat having aposition demanding more heat and a position demanding less heat, meansoperating when the thermostat is in the position demanding more heat formoving the grate to the rearward position to direct the draft throughthe air passages into the fuel l bed and means operating when thethermostat is in the position demanding less heat for reciprocating thegrate to its forward position to divert the draft through the by-passopening. '7. A furnace having iire and ash compartments and a compositegrate between the compartments comprising relatively movable members,said grate lhaving openings at intervals which are open in one positionof the members for passing .air through the fuel bed and having aby-pass opening which is open in another position of the members forby-passing air around the fuel bed,` and thermostatically controlledmeans having .a position demanding less heat and a position demandingmore heat for relatively shifting the said members back and forth,

v progressing the fuel bed'toward the bil-pass openand not through thefuel bed when said means demands less heat and passing the air throughthe fuel bed when said means demands more heat, and for deliveringadditional fuel into the furnace.

8. 4A furnace having fire and ash'compartments and a composite floorbetween the compartments comprising a grate shiftable back and forth'andnormally supporting the main body of the fuel, and structure sealingagainst the back edge of the grate in the back position thereof andsealing the side and forward portions of the grate in both positionsthereof but leaving a by-pass opening at the back edge of the grate whenit is in its forward position, and thermostatically controlled means forshifting the grate back and forth, progressing the fuel bed toward theby-` pass opening, passing the air through the by-pass opening and notthrough the fuel bed when the thermo'static means demands less heatandpassing the air through the fuel bed when the thermostatlc means demandsmore heat, and means for delivering additional fuel into the furnace.

9. A heater burning solid fuel on natural draft, including asubstantially horizontal grate having air passages through the grate,means for supporting, guiding and reciprocating the grate, there beingaby-pass opening open-behindthe grate at one limiting `positionand'closed by the grate in the other limiting position, there beingconsiderable air ow through the passages in the grate and through thefuel bed in the high heatingv position and there being bypassing of airthrough the by-pass opening in the checking position, a Stokerdevicecharging fuel labove the forward end of the grate, a thermostathaving a position demanding less heat and a positiondemanding more heat,'means operatively connecting' the thermostat, the grate and the stokerfor moving the grate into the forward position, discharging ash throughthe by-pass opening and bypassing the draft around the fuel bed andretracting the stoker when the thermostat demands less heat` and meansoperatively connecting the thermostat, the grate and the stoker formoving the grate into the high heating position and operating the stokerto introduce a charge of fuel when the thermostat demands more heat.

10. A heater burning solid fuel, including cornlbustion and ashchambers, a grate having major and minor air passages, supports for thegrate permitting the grate to reciprocate between linuting positions,structure surrounding and sealing against air flow between the ash andcombustion chambers around the grate except for a by-pass air space leftbetween the combustion chamber and the ash chamber in one limitingposition, closures obstructing the major air passages when the by-passair space is open, in the other limiting position the by-pass air spacebeing closed and the major grate air passages being open, electriccircuits respectively demanding more heat and less heat, a thermostatwhich selectively comchanical connections from the motor to the switcharm for throwing the switch arm to the other circuit when the motor isoperating in one circuit.

.tive to divert air from 11. A heater burning solid fuel, includingcombustion and ash chambers, a grate having major and minor air passagesand supporting a fuel bed, supports for the grate permitting the grateto reciprocate between limiting positions, structure surrounding andsealing against air flow between the ash and combustion chambers aroundthe grate except for a by-pass vair space left between the combustionchamber and the ash chamber in one limiting position, closuresobstructing the major air passages when the bypass air space is open, inthe other-limiting position the by-pass air space beingl closed and themajor grate air passages being open, electric circuits respectivelydemanding more heat and less heat, a thermostat which selectivelycompletes the electric circuit demanding more heat or the electriccircuit demanding less heat, an electric motor connected selectively inone or the other of said electric circuits by the thermostat, a switchhaving a switch arm which is connected alternately in one or the otherof said electric circuits, mechanical connections from the motor to thegrate for reciprocating the grate and mechanical connections from themotor to the switch arm throwing the switch arm to the other circuitwhen the motor is caused to operate in one circuit, a stoker having astoker plate and mechani-` cal connections between the motor and thestoker plate moving the stoker plate toward the fuel b'ed when thethermostat demands more heat and away from the fuel bed when thethermostat demands less heat.

12. A furnace having fire and ash compartments and a composite floorbetween the com- -partments comprising a grate having air openings andwhich is shiftable back and forth and normally supports the main body ofthe fuel, and sealing structure overlapping the sides and front of thegrate, open intermediate the overlapping portions and at the back edgeof its opening adaptedr to seal against the back of the grate when thegrate is in its rearward position and to leave a. by-pass opening whenthe grate is in its forward position, and means for shifting the gratebetween its back and forth positions to render the by-pass openingeffective or ineffective to divert air from passing through the open-'ings into the fuel bed.

13. A'furnace having fire and ash compartments and a composite `floorbetween the compartments comprising a grate shiftableback and forth andnormally supporting the main body oi' the fuel and sealingl structureoverlapping 4the sides and front of the grate, open intermediate theoverlapping portions and at the back edge of its opening adapted to sealagainst the back of the grate when the grate isin its rearwardr positionand to leave a by-pass opening when the grate is in its forwardposition, the grate havlngunder the opening of said structure laterallyspaced rows of major air passages, laterally spaced strips under theister with the rows of, and close the majorr air passages when the grateis in its forward position and the by-pass is open and means forshifting the grate between its back and forth positions to render theby-pass opening effective or ineffecpassing through the openings intothe fuel bed..n

14.\A furnace having re and ash compartments and a composite doorvbetween the compartments comprising a grate shiftable back and t forthfor normally supporting the main body of the fuel and sealingstructureoverlapping the grate and located to regminor air passagesvintermediatethe said rows.,

laterally spaced strips under the grate located to register across themajor air passages when the grate is in its forward position and thebypass is open and across certain of the minor air passages when thegrate is in its rearward position and means for shifting the gratebetween its back and forth positions to render the bypass openingeffective or ineffective to divert air from passing through the openingsinto the fuel bed.

l5. A furnace having re and ash compartments and a composite floorbetween the compartments comprising a grate having air openingsshiftable back and forth and normally supporting the main body of thefuel and structure overlapping the sides and front of the grate, openintermediate the overlapping portions and at the back edge of itsopening adapted to seal against the back of the grate when the grate lsin its rearward position and to .leave a by-pass opening when the grateis in its forward position, a floorsupport within the ash compartmentand including posts under the stucture at portions thereof laterallybeyond the grate, rollers beneath the grate and cross connectionsbetween the posts' to determine whether or not the by-pass openingl iseffective to divert air from passing through the fuel bed.

16. A furnace having ire and ash compartments and a composite gratebetween the compartments comprising relatively movable members, saidgrate having openingsA at intervals which are open in one position of.the members for passing air through the fuel bed and having a by-passopening which is open in another posi- ,tion of the members forby-passing air around the fuel, bed, and means having a positiondemanding less heat and a position demanding more heat for relativelyshifting the said members, progressing the fuel bed toward the bypassopening, passing the air through the by? mechanism operativelyconnecting one of thel members and the motor and an operative connectionbetween the motor and stop switch.

17. A heater, a furnace for the heater andA having flre and ashcompartments and a composite grate between the compartments comprisingrelatively movable members, said grate having openings at intervalswhich are open in one position of the members for passing air throughthe fuel bed and having a by-pass opening which is open in anotherposition ofthe members for by-passing air around the fuel bed, and meanshaving a position demanding less heat and a position demanding more heatfor'relatively shifting theA said members, progressing the fuel bed`to-Ward the by-pass opening, passing thev air through aliases bed when saidmeans demands less heat and n passing the air through the fuel bed whensaid means demands more heat and said means including a motor, a sourceof current, a stop switch, a thermostatic three-way switch, two way moreheat, and less heat" conductors between the switches, an aquastat switchconnected nor-- mally to close the more heat conductor and atabnormally. high temperature of the water to open the said more heaconductor while connecting the less hea conductor to the thermovstaticswitch, a circuit including the source, the

switches and the motor, mechanism operatively connecting one ofthemembers and the motor f and an operative connection between the motorand the stop switch. 18. A furnace having fire and ash compartments, amovable grate therebetween supporting the main bed of burning fuel,mechanism forv shifting the grate to and from its backward and forwardpositions, structure relatively sealing the compartments along the sidesand front of the grate when the grate is either forward or back andalong the back of the grate when the grate is in its rearward positionand leaving a by-pass opening back of the grate between the compartmentswhen the grate is ln its forward position, a fuel hopperand spout havingdelivery into the furnace above the forward portion of the grate, havinga oor of the hopper overlapping the floor of the spout, a downwardlyadjustable gate in the spout, mechanism for shifting the hopper floortoward and away from the furnace and thermostatically controlled commonmeans operating the said mechanisms with demand for more heat at thethermostat to shift the furnace grate back and the hopper floor towardthe furnace and with demand for less heat at the,V thermostat to shiftthe furnace grate forward and the hopper floor away from the furnace.

19. A furnace including a movable grate which has openings for airpassing through the fuel bed in its high heating position and opens aby-pass for the air in its fire checking position, in combination with astoker operatively connected with the furnace, a thermostat having amore heat and a less heat position, means for shifting the grate to thehigh heating position when the thermostat demands more heat, meanseffective while the thermostat demands more heat for opierating thestoker at timed intervalsto supply fuel to the me and means for movingthe grate Itoits fire checkingposition to divert the draft through theby-pass opening when the thermostat demands less heat.

20. A furnace including a movable grate which has openings for airpassing through the fuel bed inr its .high heating position and opens aby-pass for the air in its re checking position, a stoker operativelyconnected to the furnace, a thermostat having a more heat and aless'heat position, means operated by the Stoker for concurrently movingthe grate to its high heating position and moving the stoker to itsposition for charging fuel on the fire when the thermostat demands moreheat, means operative at timed intervals while the thermostat isdemanding more heat to concurrently move the grate to its firecheckinglpositicn to divert the draft through the by-pass andthe stokerto its retracted position and then to vconcurrently move the grate toits ANDREW CQMUIR.

WILLIAM c. GRIFFITHS.

